Wireless communication devices allow users to communicate via wireless telecommunication signals. A wide variety of wireless techniques have been developed to facilitate such communication. Examples of wireless communication techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), as well as a number of other techniques. One common wireless communication device is a mobile radiotelephone. Another common wireless communication device is a direct two-way communication device. A variety of other wireless devices and gadgets can similarly incorporate wireless communication capabilities.
In order to facilitate “hands free” communication on a wireless communication device, headsets have been developed. A headset typically includes a microphone and one or more speakers that are worn by the user. The speakers provide audio output to the user, and the microphone allows the user to speak into the headset. The headset couples to the wireless communication device so that audio signals can be sent to and from the user. For example, the headset may couple to the wireless communication device via an earphone and/or microphone port of the communication device. Different types of interfaces have been developed to allow different headsets to communicatively couple to different wireless communication devices. Hands-free communication is particularly useful in settings where the user needs to maintain use of his or her hands, such as when driving a vehicle or when operating machinery.
In order to allow for headset attachment to a wireless communication device, the wireless communication device typically includes a connector circuit and a signal conditioning circuit. The connector circuit provides the physical interface for electrical coupling between the device and the headset. The signal conditioning circuit provides basic analog signal conditioning to signals sent to and from headset. For example, the signal conditioning circuit may provide a bias voltage needed to properly bias the microphone. In addition, the signal conditioning circuit includes channels with amplifiers for amplifying audio signals sent to drive the speakers.
In the connector circuit, blocking capacitors are often included in the speaker channels to prevent DC signals from flowing through the headset speakers, whose return path typically couples to ground. A blocking capacitor and speaker essentially form a high pass filter that allows high frequency signals in the channels to pass through the speaker but blocks lower frequency and DC signals. Increasing the capacitance of the blocking capacitors can help avoid frequency loss in the audio signal delivered to the speakers. Use of large blocking capacitors, however, can add significant cost to the circuit and may take up valuable circuit space in the device.